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Abstract:

The present invention provides an ultraviolet-curable composition that
inhibits deterioration of a reflective layer during environmental changes
in humidity and temperature even when using silicon or a silicon compound
for the light reflecting layer, and an optical disc enabling preferable
reading and writing of recording signals even during environmental
changes in humidity and temperature.
In particular, occurrence of deterioration at the interface between a
cured coating film of an ultraviolet-curable composition and a silicon
reflective layer can be decreased and the formation of minute
white'spots, for which there is the risk of impairing reading and writing
of signals, can be effectively inhibited even in a high-temperature and
high-humidity environment by using an ultraviolet-curable composition
comprising a (meth)acrylate oligomer, a (meth)acrylate monomer and an
antioxidant, wherein the antioxidant is an antioxidant having an
isocyanuric acid backbone, and the chlorine content in the composition is
less than 120 ppm.

Claims:

1. An ultraviolet-curable composition for an optical disc comprising a
(meth)acrylate oligomer, a (meth)acrylate monomer and an antioxidant,
wherein the antioxidant is an antioxidant having an isocyanuric acid
backbone, and the chlorine content in the composition is less than 120
ppm.

2. The ultraviolet-curable composition for an optical disc according to
claim 1, wherein the antioxidant is represented by formula (1):[Chemical
1]X--[--Y-Z]3 (1)[in formula (1), X represents a trivalent group
represented by formula (2): ##STR00004## Y represents a divalent group
represented by formula (3):[Chemical 3]--(CH2)n-- (3)(in
formula (3), n is 1 to 3), and Z represents a monovalent group
represented by formula (4): ##STR00005## (in formula (4), R1 and
R2 each independently represent a methyl group or tert-butyl group,
at least one of R1 and R2 represents a tert-butyl group, and
R3 and R4 each independently represent a hydrogen atom or a
methyl group), or by formula (5): ##STR00006## (in formula (5), R5
and R6 each independently represent a methyl group or tert-butyl
group, at least one of R5 and R6 represents a tert-butyl group,
and R7 and R8 each independently represent a hydrogen atom or a
methyl group)].

3. An optical disc having a light reflecting layer composed of silicon or
a silicon compound and having a cured coating film of an
ultraviolet-curable composition on the light reflecting layer, wherein
the ultraviolet-curable composition is the ultraviolet-curable
composition for an optical disc according to claim 1.

4. An optical disc having a light reflecting layer composed of silicon or
a silicon compound and having a cured coating film of an
ultraviolet-curable composition on the light reflecting layer, wherein
the ultraviolet-curable composition is the ultraviolet-curable
composition for an optical disc according to claim 2.

Description:

CROSS REFERENCE TO PRIOR APPLICATIONS

[0001]This is a U.S. patent application claiming priority to a Japanese
Patent Application No. 2008-216545, filed Aug. 26, 2008 which is
incorporated by reference herein.

BACKGROUND ART

[0002]Digital Versatile Discs (DVDs), which constitute the mainstream of
high-density recordable optical discs, have a structure in which two
substrates having a thickness of 0.6 mm are laminated with an adhesive. A
laser having a shorter wavelength of 650 nm is used and a higher
numerical aperture is used for the optical system of DVD in order to
achieve higher density when compared to Compact Discs (CDs).

[0003]Although there are various variations in the process used to produce
DVDs, they are basically produced by a method in which at least one
substrate has an information recording layer and two substrates are
laminated together, and at that time, an ultraviolet-curable composition
is used as an adhesive.

[0004]In the case of a read-only use DVD, DVDs are classified in the
manner of DVD-5, DVD-10, DVD-9 or DVD-18 according to differences in the
constitution of the two laminated substrates. Although the details of
these constitutions are disclosed by known documents (see, for example,
Japanese Unexamined Patent Application, First Publication No. H10-3699
and Japanese Unexamined Patent Application, First Publication No.
2001-266419), an overview thereof is described below.

[0005]Concave-convexes known as pits corresponding to recorded information
are provided in one side of both of the two laminated substrates, and an
information recording layer (also referred to as a reflective layer) is
formed by providing a film that reflects laser light for reading
information in the form of an aluminum layer so as to cover the
concave-convexes of the pits. A DVD in which this is used as a reflective
film of laser light and two information recording layers are laminated in
opposition is classified as "DVD-10", that in which one of the two layers
uses a transparent substrate that does not have an information recording
layer is classified as "DVD-5", and that in which concave-convexes of
pits corresponding to recorded information are provided on one substrate
and a translucent reflective layer composed of gold or silicon compound
(information recording layer) is formed so as to cover the pits, while an
aluminum reflective layer (information recording layer) is formed on the
other substrate is classified as "DVD-9". Moreover, that having a
structure in which two substrates each having two layers consisting of a
reflective layer and a translucent reflective layer on one side are
laminated is classified as "DVD-18". These DVDs are used according to the
particular application.

[0006]In optical discs such as DVDs, silver or silver alloys and silicon
or silicon compounds are used for the transparent or translucent light
reflecting layer, and a curable coating film of an ultraviolet-curable
composition is widely used for the light transmitting layer that protects
the light reflecting layer or adhesive layer that laminates a substrate
having a light reflecting layer. Although silicon or a silicon compound
is inexpensive, when silicon or a silicon compound is used for the light
reflecting layer of an optical disc, the surface of the light reflecting
layer became cloudy in a high-temperature and high-humidity environment,
causing impairment during reading and writing of signals depending on the
laminated ultraviolet-curable composition.

[0007]In order to resolve this problem, an ultraviolet-curable resin
composition using
oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone] for the
photopolymerization initiator is disclosed as an ultraviolet-curable
resin composition capable of forming an optical disc having high
durability even when using silicon or a silicon compound for the light
reflecting layer (see Japanese Unexamined Patent Application, First
Publication No. 2005-68348). This composition is a composition that is
able to inhibit clouding of the silicon reflective film during
environmental changes in humidity and temperature by using a specific
photopolymerization initiator.

[0008]However, although this ultraviolet-curable composition is able to
prevent clouding by visual observation during environmental changes in
humidity and temperature, minute white spots are sporadically observed in
microscopic observations of the silicon reflective layer surface, thereby
impairing reading and writing of information in optical discs requiring
even higher density recording.

SUMMARY OF THE INVENTION

[0009]An object of the present invention is to provide an
ultraviolet-curable composition that inhibits deterioration of a
reflective layer during environmental changes in humidity and temperature
even when using silicon or a silicon compound for the light reflecting
layer, and to provide an optical disc enabling preferable reading and
writing of recording signals even during environmental changes in
humidity and temperature.

[0010]The ultraviolet-curable composition of the present invention is able
to decrease occurrence of deterioration at the interface of a cured
coating film of the ultraviolet-curable composition and a silicon
reflective layer and effectively inhibit the formation of minute white
spots for which there is the risk of impairing reading and writing of
signals even in a high-temperature and high-humidity environment, by
containing an antioxidant having an isocyanuric acid backbone having high
affinity for a silicon reflective layer surface in a composition in which
the content of chlorine components, which are presumed to be one of the
factors responsible for deterioration of the silicon reflective layer
surface, has been decreased.

[0011]Namely, the present invention provides an ultraviolet-curable
composition for an optical disc comprising a (meth)acrylate oligomer, a
(meth)acrylate monomer and an antioxidant, wherein the antioxidant is an
antioxidant having an isocyanuric acid backbone, and the chlorine content
in the composition is less than 120 ppm.

[0012]Since the ultraviolet-curable composition for an optical disc of the
present invention is able to inhibit minute deterioration occurring in
the silicon reflective layer surface that is not inhibited by
compositions of the prior art, signal characteristics can be expected to
be improved, thereby making this useful for an optical disc enabling
preferable reading and writing of signals when applied to an optical disc
for high-density recording.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 shows the results of observing appearance following
durability testing of an optical disc produced in Example 1 of the
present invention (magnification: 25×).

[0014]FIG. 2 shows the results of observing appearance following
durability testing of an optical disc produced in Example 3 of the
present invention (magnification: 25×).

[0015]FIG. 3 shows the results of observing appearance following
durability testing of an optical disc produced in Comparative Example 1
of the present invention (magnification: 25×).

[0016]FIG. 4 shows the results of observing appearance following
durability testing of an optical disc produced in Comparative Example 3
of the present invention (magnification: 25×).

DETAILED DESCRIPTION OF THE INVENTION

[0017]The ultraviolet-curable composition for an optical disc of the
present invention contains a (meth)acrylate oligomer, a (meth)acrylate
monomer and an antioxidant, the antioxidant is an antioxidant having an
isocyanuric acid backbone, and the chlorine content in the composition is
less than 120 ppm.

[0018][(Meth)acrylate Oligomer]

[0019]Various types of oligomers used in the light transmitting layer or
adhesive layer of an optical disc can be used for the (meth)acrylate
oligomer used in the present invention and urethane (meth)acrylate and
epoxy (meth)acrylate can be used preferably.

[0020]In the present invention, since it is easy to prepare an oligomer
having a low chlorine content, urethane (meth)acrylate is preferably used
for the (meth)acrylate oligomer.

[0021]Urethane (meth)acrylate obtained from, for example, compounds having
two or more isocyanurate groups in a molecule thereof, compounds having a
hydroxyl group and a (meth)acryloyl group, and compounds having two or
more hydroxyl groups in a molecule thereof can be preferably used for the
urethane (meth)acrylate. In addition, urethane (meth)acrylate obtained by
reacting a compound having a hydroxyl group and a (meth)acryloyl group
with a compound having two isocyanurate groups in a molecule thereof can
also be used preferably.

[0022]Examples of compounds having two or more isocyanurate groups in a
molecule thereof include polyisocyanates such as tetramethylene
diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene
diisocyanate, bis(isocyanatomethyl) cyclohexane, cyclohexane
diisocyanate, bis(isocyanatocyclohexyl) methane, isophorone diisocyanate,
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylene
diisocyanate, diphenylmethane diisocyanate or m-phenylene diisocyanate.
In particular, diisocyanate compounds having two isocyanate groups in a
molecule thereof can be used preferably, and tolylene diisocyanate is
particularly preferable since it does not demonstrate exacerbation of hue
or decreases in light transmittance.

[0023]Examples of compounds having a hydroxyl group and a (meth)acryloyl
group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate
and hydroxybutyl (meth)acrylate, as well as compounds obtained by
reacting these (meth)acrylates with compounds having two or more hydroxyl
groups. Other examples include compounds obtained by reacting compounds
having two or more hydroxyl groups with (meth)acrylic acid, such as
addition reaction products of glycidyl ether compounds and (meth)acrylic
acid, or mono(meth)acrylates of glycol compounds.

[0024]Polyols are preferably used as compounds having two or more hydroxyl
groups, and specific examples thereof include high molecular weight
polyols in the form of oligomers of alkylene polyols and the like, such
as ethylene glycol, 1,2-propanediol, 1,3-propanediol,
2-methyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol,
1,5-pentanediol, 2-methyl-1,5-pentanediol, neopentyl glycol,
3-methyl-1,5-pentanediol, 2,3,5-trimethyl-1,5-pentanediol,
1,6-hexanediol, 2-ethyl-1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol,
1,8-octanediol, trimethylolpropane, pentaerythritol, sorbitol, mannitol,
glycerin, 1,2-dimethylolcyclohexane, 1,3-dimethylolcyclohexane or
1,4-dimethylolcyclohexane.

[0025]In particular, polyether polyols having ether bonds, polyester
polyols having ester bonds obtained by a reaction with a polybasic acid
or a ring-opening polymerization of a cyclic ester, or polycarbonate
polyols having carbonate bonds obtained by a reaction with a carbonate
are preferable. At least a portion of these polyols, preferably 15 mol %
or more of the total amount of the polyols, and more preferably 30 mol %
or more of the total amount of the polyols, preferably has a molecular
weight of 500 to 2500.

[0026]In addition to oligomers of the aforementioned polyols, examples of
polyether polyols include polytetramethylone glycol in the form of a
ring-opened polymer of a cyclic ether such as tetrahydrofuran, and
alkylene oxide addition products of the aforementioned polyols, such as
ethylene oxide, propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide,
2,3-butylene oxide, tetrahydrofuran, styrene oxide or epichlorhydrin.

[0027]Examples of polyester polyols include reaction products of the
aforementioned polyols with polybasic acids such as maleic acid, fumaric
acid, adipic acid, sebacic acid or phthalic acid, and polycaprolactones
in the form of ring-opened polymers of cyclic esters such as
caprolactone.

[0029]Although one type of polyol may be used or two or more types of
polyols may be used in combination, urethane (meth)acrylate, which
combines the use of two or more types of polyether polyols, polyester
polyols and polycarbonate polyols, is preferable, and two types of
polyols are more preferably used in combination. The combined use of
these polyols preferably facilitates adjustment of deformation resistance
or surface hardness of the resulting cured film in a high-temperature and
high-humidity environment. Preferable examples of the combined use of two
types include a polyester polyol and a polycarbonate polyol in the case
of increasing surface hardness, and the combined use of a polyether
polyol in the case of improving deformation resistance at a
high-temperature and high-humidity. The combined use of a polyether
polyol and a polycarbonate polyol is preferable in the case of obtaining
intermediate properties thereof.

[0030]The content of each polyol in the case of combining the use of
polyols is such that the content of polyether polyol is preferably 20 to
90% by weight and more preferably 30 to 80% by weight based on the total
weight of the polyols used. The content of polyester polyol is preferably
10 to 70% by weight and more preferably 20 to 60% by weight. As a result
of making the contents of polyether polyol and polyester polyol to be
within these ranges, surface hardness as well as humidity and heat
resistance of the cured product can be easily obtained.

[0031]Preferable examples of the urethane (meth)acrylate used in the
present invention include urethane acrylates having a polyether backbone
such as FAU-742TP and FAU-306 manufactured by DIC Corp., urethane
acrylates having a tolylene diisocyanate backbone such as FAU-1000
manufactured by DIC Corp., and urethane acrylates having a polyester
backbone such as Photomer 6892 manufactured by Cognis Japan, Ltd. or
Ebecryl 8405 manufactured Daicel-Cytec Co., Ltd.

[0032]The content of the urethane (meth)acrylate in the
ultraviolet-curable composition of the present invention is preferably 20
to 70% by weight and more preferably 30 to 60% by weight in the
ultraviolet-curable compounds contained in the ultraviolet-curable
composition. As a result of making the urethane (meth)acrylate content to
be within these ranges, suitable flexibility can be imparted to the cured
film.

[0033]The weight average molecular weight (Mw) of the urethane
(meth)acrylate used in the present invention as measured by gel
permeation chromatography (GPC) is preferably 300 to 4000 and more
preferably 400 to 3000. As a result, an optical disc using the
ultraviolet-curable composition of the present invention has even better
durability.

[0034]Furthermore, weight average molecular weight as determined by GPC is
determined by using the HLC-8020 system manufactured by Tosoh Corp.,
using the GMHx1-GMHx1-G200Hx1-G1000Hx1w for the column, using THF for the
solvent, measuring at a flow rate of 1.0 ml/min, column temperature of
40° C. and detector temperature of 30° C., and based on the
standard polystyrene conversion.

[0035]In the present invention, although a composition that is
substantially free of epoxy (meth)acrylate for the (meth)acrylate
oligomer is preferable since this facilitates adjustment of the chlorine
content in the composition, epoxy (meth)acrylate can also be used
preferably provided it does not cause an increase in the chlorine content
of the composition. There are no particular limitations on the epoxy
(meth)acrylate provided it is obtained by a reaction between a compound
having one or more epoxy groups in a molecule thereof and acrylic acid,
and may be modified by polyester, polyether or rubber and the like.

[0036][(Meth)acrylate Monomer]

[0037]In the present invention, the use of a (meth)acrylate monomer, such
as a (meth)acrylate having a (meth)acryloyl group in a molecule thereof
(to be abbreviated as monofunctional (meth)acrylate), a (meth)acrylate
having two (meth)acryloyl groups in a molecule thereof (to be abbreviated
as difunctional (meth)acrylate), or a (meth)acrylate having three or more
(meth)acryloyl groups in a molecule thereof (to be abbreviated as
polyfunctional (meth)acrylate), in combination with the aforementioned
(meth)acrylate oligomer enables the obtaining of a composition having a
desired viscosity and elastic modulus after curing.

[0043]In addition, ultraviolet-curable compounds such as
N-vinylpyrrolidone, N-vinylcaprolactam or vinyl ether monomers can be
used as necessary.

[0044]The content of monofunctional (meth)acrylate contained in the total
amount of ultraviolet-curable compounds contained in the
ultraviolet-curable composition in the present invention is preferably 3
to 30% by weight and more preferably 5 to 25% by weight. The content of
difunctional (meth)acrylate is preferably 3 to 30% by weight and more
preferably 5 to 20% by weight. In addition, the content of trifunctional
or more highly functional (meth)acrylate is preferably 25% by weight or
less and more preferably 20% by weight or less.

[0045][Antioxidant]

[0046]In the present invention, an antioxidant having an isocyanuric acid
backbone is used for the antioxidant. Since the isocyanuric acid backbone
in the antioxidant has high affinity for silicon or silicon compounds,
adhesion is favorable at the interface between a cured coating film of an
ultraviolet-curable composition containing this antioxidant and silicon
or silicon compounds. As a result, the occurrence of
deterioration-causing penetration of silicon or silicon compound onto the
surface of the light reflecting layer in a high-temperature and
high-humidity environment, along with the occurrence of deterioration,
can be preferably inhibited, thereby making it possible to decrease the
formation of minute white spots.

[0047]Antioxidants represented by formula (1), for example, can be
preferably used for the antioxidant having an isocyanuric acid backbone.

[0052](wherein, n is 1 to 3), and Z represents a monovalent group
represented by formula (4):

##STR00002##

[0053](wherein, R1 and R2 each independently represent a methyl
group or tert-butyl group, at least one of R1 and R2 represents
a tert-butyl group, and R3 and R4 each independently represent
a hydrogen atom or a methyl group), or by formula (5):

##STR00003##

[0054](wherein, R5 and R6 each independently represent a methyl
group or tert-butyl group, at least one of R5 and R6 represents
a tert-butyl group, and R7 and R8 each independently represent
a hydrogen atom or a methyl group)].

[0055]Since a compound represented by formula (1) has a structure
represented by formula (4) or formula (5) in which an easily oxidized
hydroxyl group is adjacent to a tert-butyl group that inhibits oxidation
of the hydroxyl group, and that structure is arranged centering about the
isocyanuric acid backbone represented by the aforementioned formula (2),
it is able to preferably inhibit deterioration of silicon or silicon
compounds.

[0056]In particular, since an antioxidant, in which Z in formula (1) has a
structure represented by formula (4) and R1 and R2 in formula
(4) are both tert-butyl groups, has an easily oxidized hydroxyl group on
the terminal thereof and has a structure in which tert-butyl groups are
adjacent to the hydroxyl group on both sides thereof, it preferably
demonstrates oxidation controlling effects, and is preferable since it is
able to particularly preferably inhibit deterioration of silicon or
silicon compounds, with a compound in which n in formula (3) is 1 being
particularly preferable. Commercially available examples of compounds
represented by formula (1) include Irganox 3114 and Irganox 3790 (both
manufactured by Ciba Specialty Chemicals Inc.).

[0057][Ultraviolet-Curable Composition]

[0058]The ultraviolet-curable composition of the present invention
contains the aforementioned (meth)acrylate oligomer, the (meth)acrylate
monomer and the antioxidant, and is an ultraviolet-curable composition
for an optical disc in which the chlorine content in the composition is
less than 120 ppm. In the present invention, together with using a
compound represented by the aforementioned formula (1), by making the
chlorine content less than 120 ppm, preferably less than 110 ppm and more
preferably less than 105 ppm, oxidation of silicon or silicon compounds
that progresses at a high-temperature and high-humidity can be prevented,
and deterioration of silicon or silicon compounds can be preferably
inhibited.

[0059]The chlorine content in the composition is measured using the ZSX
Purimus wavelength dispersive X-ray fluorescence spectrometer
manufactured by Rigaku Corp., using a beryllium filter in a helium
atmosphere, setting the fixed-angle measurement elements to chlorine,
sulfur, phosphorous, silicon and sodium, setting the angle fixation time
to 20 seconds each for both peak and background, using an irradiated
surface area of 30 mmφ in diameter, and measuring using the total
element qualitative analysis and fixed-angle measurement mode. Chlorine
content is determined according to the thin film FP method.

[0060]A coating film can be preferably formed by making the viscosity of
the ultraviolet-curable composition of the present invention is 200 to
1000 mPas and preferably 300 to 800 mPas.

[0061]The elastic modulus of a cured film after irradiating the
ultraviolet-curable composition of the present invention with ultraviolet
light is preferably adjusted to be 100 to 3000 MPa (at 25° C.). In
particular, a composition in which the elastic modulus is 200 to 2500 MPa
is more preferable. If the elastic modulus of the composition is within
these ranges, strain during curing is easily alleviated, thereby allowing
the obtaining of an optical disc having a small change in warping even
when exposed to a high-temperature and high-humidity environment for a
long period of time. In addition, the elastic modulus of the cured film
is preferably adjusted to 200 to 2500 MPa (at 25° C.), and if the
modulus of elasticity of the composition is within this range, there is
little deterioration of the error rate of recording signals when forming
the optical disc, thereby facilitating the formation of an optical disc
having superior reliability.

[0062]In addition to the aforementioned (meth)acrylate oligomer,
(meth)acrylate monomer and antioxidant, known photopolymerization
initiators, thermal polymerization initiators and the like can be used in
the ultraviolet-curable composition for an optical disc of the present
invention.

[0063]Examples of photopolymerization initiators are able to be used in
the present invention including molecular cleavage types such as benzoin
isobutyl ether, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, benzyl
1-hydroxycyclohexyl phenyl ketone, benzoin ethyl ether, benzyl dimethyl
ketal, 2-hydroxy-2-methyl-1-phenylpropan-1-one,
1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one,
2,4,6-trimethylbenzoyldiphenyl phosphine oxide or
2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one; and hydrogen
abstraction types such as benzophenone, 4-phenylbenzophenone,
isophthalophenone or 4-benzoyl-4'-methyl-diphenylsulfide.

[0064]A surfactant, leveling agent, thermal polymerization inhibitor,
hindered phenols, phosphites and other antioxidants or hindered amines
and other light stabilizers can also be added as necessary to the
ultraviolet-curable composition used in the present invention. In
addition, trimethylamine, methyl dimethanolamine, triethanolamine,
p-dimethylaminoacetophenone, ethyl p-dimethylaminobenzoate, isoarnyl
p-dimethylaminobenzoate, N,N-dimethylbenzylamine and
4,4'-bis(diethylamino)benzophenone, for example, can be used as a
sensitizer. Moreover, amines not causing an addition reaction with the
aforementioned photopolymerizable compounds can also be used in
combination.

[0065][Optical Disc]

[0066]The optical disc of the present invention has a light reflecting
layer composed of silicon or silicon compound, and employs a constitution
in which a cured coating film of the aforementioned ultraviolet-curable
composition for an optical disc is laminated directly on the light
reflecting layer. As a result of employing this constitution, the optical
disc using the ultraviolet-curable composition of the present invention
is resistant to deterioration of the light reflecting layer, which
becomes an impairment when reading and writing signals even at a
high-temperature and high-humidity, and is able to preferably read and
write audio and video signals as well as other special signals and the
like.

[0067]An optical disc having this structure is an optical disc having, for
example, a structure in which a first reflective film for reflecting
laser light for reading information is provided on a first substrate, and
a resin layer composed of a cured film of the aforementioned
ultraviolet-curable composition is further provided on the first
reflective film. The optical disc of the present invention is an optical
disc employing such a structure or an optical disc partially employing
that structure. Examples of such optical discs include CD-ROM or CD-R
having a light reflecting layer composed of silicon or a silicon
compound, and provided with a protective layer in the form of a resin
layer composed of a cured film of the ultraviolet-curable composition on
the light reflecting layer. In addition, another example is a DVD-5 in
which a substrate having a light reflecting layer composed of silicon or
a silicon compound is laminated with another substrate composed of an
ultraviolet-curable composition by using the light reflecting layer as an
adhesive surface.

[0068]In addition, the optical disc using the ultraviolet-curable
composition for an optical disc of the present invention may also be an
optical disc having a structure in which a second substrate, which is
provided with a second reflective film for reflecting laser light for
reading information, is further provided on the resin layer composed of a
cured film of the ultraviolet-curable composition provided on the first
reflective film so that the resin layer and the second reflective film
make contact. Examples of an optical disc having such a structure include
DVD-9, DVD-18, DVD-10 and other laminated-type optical discs in which at
least one of the two optical disc substrates provided with a reflective
layer for reflecting laser light for reading information has a light
reflecting layer composed of silicon or a silicon compound on the surface
thereof, and the two optical disc substrates are laminated by using the
light reflecting layers of the two substrates as adhesive surfaces.

[0069]A disc-shaped, circular resin substrate can be used as a substrate,
and polycarbonate can be used as a preferable example of a resin. In the
case the optical disc is for read-only, pits responsible for recording
information on the substrate are formed in the surface that is laminated
with the light reflecting layer.

[0070]The resin layer composed of the aforementioned ultraviolet-curable
composition present in the optical disc preferably efficiently transmits
light, and total light transmittance at a thickness of 50 μm is
preferably 85% or more and particularly preferably 90% or more.

[0071]The thickness of the resin layer may be a thickness that is suitable
based on the constitution of the optical disc, and in the case the
optical disc is a DVD-9, for example, the thickness of the resin layer is
preferably 40 to 70 μm.

[0072]The type of optical disc is preferably a read-only DVD in the form
of a "DVD-5", "DVD-10", "DVD-9" or "DVD-18", and particularly preferably
a read-only DVD in the form of a "DVD-9".

[0073]In the case the ultraviolet-curable composition coated onto the
light reflecting layer is cured by irradiating with ultraviolet light,
irradiation can be carried out by a continuous light irradiation system
using, for example, a metal halide lamp or high-pressure mercury lamp, or
can be carried out by a flashlight irradiation system as described in
U.S. Pat. No. 5,904,795. A flashlight irradiation system is more
preferable with respect to enabling efficient curing.

[0074]In the case of irradiating with ultraviolet light, the accumulated
light intensity is preferably controlled to 0.05 to 1 J/cm2. The
accumulated light intensity is more preferably 0.05 to 0.8 J/cm2 and
particularly preferably 0.05 to 0.6 J/cm2. The ultraviolet-curable
composition used in the optical disc of the present invention is
sufficiently cured even if the accumulated light intensity is low, does
not cause tacking on the edges or surface of the optical disc, and does
not cause warping or strain of the optical disc.

[0075]During the course of irradiation with ultraviolet light, irradiation
can be carried out with a continuous light irradiation system using, for
example, a metal halide lamp or high-pressure mercury lamp, or with a
flashlight irradiation system. A flashlight irradiation system is more
preferable with respect to enabling efficient curing.

[0076]The following describes examples in the case of producing a "DVD-5",
"DVD-10", "DVD-9" and "DVD-18". However, examples of the optical disc of
the present invention are not limited thereto. In addition, the
ultraviolet-curable compositions used in the following production
examples refer to ultraviolet-curable compositions containing a compound
represented by the aforementioned formula (1) used in the present
invention.

[0077](DVD-9 Production)

[0078]An optical disc substrate (A) (second substrate), in which a 40 to
60 nm metal thin film (second reflective film) was laminated on
concave-convexes known as pits responsible for recording information, and
an optical disc substrate (B) (first substrate), in which a 10 to 30 nm
translucent reflective film (translucent reflective film: first
reflective film) composed of an alloy having silicon or a silicon
compound as the main component thereof was laminated on concave-convexes
known as pits responsible for recording information, are prepared.

[0079]Furthermore, an alloy having aluminum as the main component thereof
or silver or an alloy having silver as the main component thereof, for
example, can be used for the second reflective film. In addition, a
substrate commonly known as an optical disc substrate can be used for the
optical disc substrate. Examples of substrates include amorphous
polyolefins, polymethyl methacrylate and polycarbonate, with a
polycarbonate substrate being used particularly preferably.

[0080]Next, the ultraviolet-curable composition is coated onto the metal
thin film (second reflective film) of the substrate (A) (second
substrate), and the substrate B (first substrate), on which the
translucent reflective film (first reflective film) is laminated, is
laminated with the substrate (A) (second substrate) with the
ultraviolet-curable composition coated on the surface of the metal thin
film (second reflective film) interposed there between so that the film
surface of the translucent reflective film (first reflective film) serves
as the adhesive surface, after which the one side or both sides of the
two laminated substrates is irradiated with ultraviolet light to adhere
the two and obtain a "DVD-9".

[0081](DVD-18 Production)

[0082]Moreover, after having produced the DVD-9, by separating only the
substrate (A) (second substrate) while leaving the metal thin film
(second reflective film) formed on the substrate (A) (second substrate)
on the side of the substrate (B) (first substrate), a disc intermediate
is produced in which the substrate (B) (first substrate), the translucent
reflective film (first reflective film), a cured film of the
ultraviolet-curable composition and the metal thin film (second
reflective film) are sequentially laminated in that order. Two of these
disc intermediates are prepared. Next, these two disc intermediates are
adhered by using the metal thin films (first reflective films) thereof as
adhesive surfaces so that those surfaces are in mutual opposition to
obtain a "DVD-18".

[0083](DVD-10 Production)

[0084]Two substrates for an optical disc consisting of a substrate (C1)
(first substrate) and a substrate (C2) (second substrate) are prepared in
which a 40 to 60 nm reflective film composed of an alloy having silicon
or a silicon compound as the main component thereof is laminated on
concave-convexes known as pits responsible for recording information. The
ultraviolet-curable composition is coated onto a reflective film (first
reflective film) of one of the substrates (C1) (first substrate), the
other substrate (C2) (second substrate) is laminated with the first
substrate (C1) (first substrate) with the composition coated on the
reflective film (first reflective film) of the substrate (C1) (first
substrate) interposed there between so that the film surface of the
reflective film (second reflective film) serves as the adhesive surface,
after which one or both sides of the two laminated substrates is
irradiated with ultraviolet light to adhere the two and obtain a
"DVD-10".

[0085](DVD-5 Production)

[0086]A substrate for an optical disc (D) (first substrate) is prepared in
which a 40 to 60 nm metal thin film (first reflective film) composed of
an alloy having silicon or a silicon compound as the main component
thereof is laminated onto concave-convexes known as pits responsible for
recording information. Separate from this, a substrate for an optical
disc (E) is prepared that does not have pits. The ultraviolet-curable
composition is coated onto the first reflective film of the substrate (D)
(first substrate), and the substrate (D) (first substrate) is laminated
with the substrate (E) with the composition interposed there between,
after which one or both sides of the two laminated substrates is
irradiated with ultraviolet light to adhere the two and obtain a "DVD-5".

EXAMPLES

Examples 1 to 4 and Comparative Examples 1 to 5

[0087]The raw materials of each composition were melted by heating for 3
hours at 60° C. and ultraviolet-curable compositions of each of
the examples and comparative examples were prepared according to the
blending compositions shown in the following Tables 1 and 2.

[0088]DVD-9 laminated discs were produced using the resulting
ultraviolet-curable compositions, and durability was evaluated according
to the test method described below. The results are shown in the lower
portions of Tables 1 and 2.

[0089](Measurement of Chlorine Content)

[0090]Chlorine content in the compositions was measured using the ZSX
Purimus wavelength dispersive X-ray fluorescence spectrometer
manufactured by Rigaku Corp., using a beryllium filter in a helium
atmosphere, setting the fixed-angle measurement elements to chlorine,
sulfur, phosphorous, silicon and sodium, setting the angle fixation time
to 20 seconds each for both peak and background, using an irradiated
surface area of 30 mmφ in diameter, and measuring using the total
element qualitative analysis and fixed-angle measurement mode. Chlorine
content was determined according to the thin film FP method.

[0091](DVD-9 Laminated Disc Durability Test)

[0092]The ultraviolet-curable compositions of each of the examples and
comparative examples were coated with a dispenser onto a polycarbonate
substrate in which information recording pits were formed and in which an
aluminum thin film having a thickness of 50 nm was laminated so as to
cover the pits, and a polycarbonate disc substrate, in which silicon was
laminated as a translucent reflective film, was laminated so that the
translucent reflective film contacted the ultraviolet-curable
composition. Next, the laminated disc was rotated with a spin coater so
that the film thickness of the cured film was 50 to 60 μm. Next, the
laminated disc was irradiated with ultraviolet light in air from the side
of the translucent reflective film using an ultraviolet curing device
manufactured by Eye Graphics Co., Ltd. with a metal halide lamp (equipped
with a cold mirror, lamp output: 120 W/cm) and at an accumulated light
intensity of 0.1 J/cm2 to produce DVD-9 using each of the
compositions.

[0093]The number of PI errors was measured for the produced discs at an
inner peripheral region (position: 24.50 to 25.00 mm) and intermediate
peripheral region (position: 40.03 to 40.51 mm) using the SA-300
manufactured by AudioDev AB. The average value of the inner and
intermediate peripheral regions was used for the number of PI errors.

[0094]Subsequently, an environmental test was carried out for 240 hours at
80° C. and 85% RH using the Etac constant-temperature and
constant-humidity chamber manufactured by Espec Corp. The number of PI
errors was measured for each disc following testing.

[0095]The PI error ratio (the number of PI errors after environmental
testing/the number of PI errors before environmental testing) was
determined from the number of PI errors before and after environmental
testing.

[0096]Discs in which the PI error ratio was less than 2 were evaluated as
∘, while those in which the PI error ratio was 2 or more were
evaluated as ×.

[0097](Post-Durability Test Appearance)

[0098]The appearance of the optical discs after the durability test was
confirmed using the VHX-200 Digital Microscope manufactured by Keyence
Corp (magnification: 25×).

[0099]Those discs that were free of defects were evaluated as
∘, those in which white lump-like defects were able to be
confirmed were evaluated as ×, while those in which white lump-like
defects were frequently observed were evaluated as ××.

[0100]In addition, the observation results for Examples 1 and 3 and
Comparative Examples 1 and 3 are shown in FIGS. 1 to 4.

[0101](Measurement of Elastic Modulus)

[0102]After coating the ultraviolet cured compositions onto a glass plate
to a cured film thickness of 100±10 μm, the coating films were
cured using a metal halide lamp (equipped with a cold mirror, lamp
output: 120 W/cm) and at an accumulated light intensity of 0.5 J/cm2
in a nitrogen atmosphere. The elastic modulus of the cured films was
measured as the dynamic elastic modulus E' at 25° C. by measuring
with an automated dynamic viscoelasticity measuring device manufactured
by TA Instruments Inc.

[0116]As shown in Tables 1 and 2, the produced optical discs of Examples 1
to 4, wherein chlorine content attributable to the oligomer in the
composition of the present invention was less than-120 ppm and a compound
represented by formula (1) was comprised therein, demonstrated low PI
error ratios along with favorable durability in a high-temperature and
high-humidity environment. The appearance of the optical discs following
durability testing was also free of defects.

[0117]On the other hand, Comparative Example 1, which did not contain a
compound represented by formula (1) but had a chlorine content of less
than 120 ppm, Comparative Example 2, which did not contain a compound
represented by formula (1) and had a chlorine content of 120 ppm or more,
and Comparative Examples 3 to 5, which contained a compound represented
by formula (1) and had a chlorine content of 120 ppm or more, all
demonstrated high PI error ratios, and did not exhibit durability in a
high-temperature and high-humidity environment. The appearance of these
optical discs following durability testing was such that white and
lump-like defects were observed that extended beyond the polycarbonate
substrate, resulting in a poor appearance.

Patent applications by Hirokazu Saito, Ageo-Shi JP

Patent applications by Koichi Fujii, Niiza-Shi JP

Patent applications by DIC Corporation

Patent applications in class Polymer derived from material having at least one acrylic or alkacrylic group or the nitrile or amide derivative thereof (e.g., acrylamide, acrylate ester, etc.)

Patent applications in all subclasses Polymer derived from material having at least one acrylic or alkacrylic group or the nitrile or amide derivative thereof (e.g., acrylamide, acrylate ester, etc.)